Motorized vehicles include differentials for transferring torque from a drive shaft to driven shafts attached to wheels of the vehicle. Some differentials include an overrunning clutch providing four-wheel drive capability for transmitting torque to driven shafts of the vehicle as needed. U.S. Pat. No. 6,622,837 discloses a bi-directional overrunning clutch having roll cages shifted by application of an electromagnetic field into a position providing four-wheel drive capability in which slippage of primary drive wheels causes the rolls to become wedged between the tapered surfaces of a clutch housing and a race. The wedging of the rolls results in torque transfer between the clutch housing and the race.
The clutch of the '837 patent also provides engine braking capability (“backdriving”) for use during steep descents. In the backdriving mode, the drive shaft of the vehicle becomes engaged by the driven shafts such that the drive shaft is actually driven by the driven shafts. The clutch of the '837 patent includes a clutch pack assembly having friction plates and drive plates interleaved with each other. The friction plates and drive plates are respectively engaged with the clutch housing and a driven shaft. When the backdriving feature is inactive, the friction plates and drive plates are free to rotate with respect to each other.
The clutch pack assembly of the '837 patent includes a hydraulic piston actuated by pressurized fluid from a hydraulic pressure source to apply pressure to the friction plates and drive plates. The pressure applied by the hydraulic piston forces to the friction plates and drive plates to rotate together such that the clutch housing and the driven shaft are engaged to each other. In the clutch of the '837 patent, the hydraulic pressure source supplying pressurized fluid to the clutch pack assembly is external to the clutch.